Heretofore, alumina has been mainly used as an electrically insulating ceramic material. Alumina, however, has various disadvantages. For example, alumina causes a delay in signal propagation because it has a high dielectric constant. The calcination temperature of alumina is so high that tungsten or molybdenum having a high melting point must necessarily be used as a signal conductor, even though the conductivity of tungsten or molybdenum is relatively poor. Moreover, since the coefficient of thermal expansion of ceramic is greater than that of a silicon device chip, stress and/or strain is produced in the combination thereof.
In order to overcome the above problems, the present inventors have developed a crystallized glass as disclosed in JP-A-59-92943, JP-A-59-83957, JP-B-63-6503, JP-B-63-6499 and U.S. Pat. No. 4,540,671. (The term "JP-A" as used herein means an "unexamined published Japanese patent application", and the term "JP-B" as used herein means an "examined Japanese patent publication".) The calcination temperature of the above crystallized glass is sufficiently low such that high density wiring of highly electrically conductive metals such as gold, silver or copper is practical and simultaneous calcination can be carried out. Depending on the density, speed and size of the semiconductor elements, low temperature calcination can be carried out with a crystallized glass having a low dielectric constant and a low coefficient of thermal expansion.
However the above crystallized glass ceramic is white in color and requires compounding with a coloring agent in order to protect an encased integrated circuit element from light.
If, however, an oxide coloring agent commonly used for the coloration of alumina is mixed with the above crystallized glass material and calcined, harmful components, such as cristobalite, are formed which raise the coefficient of thermal expansion of the crystallized glass produced during calcination (crystallization thermal treatment), and colored crystallized glass having the desired physical characteristics cannot be obtained.